The invention concerns the seal between a hot pipeline with a higher wall temperature t.sub.1 that extends through a nozzle of a reactor pressure vessel for example with a lower wall temperature t.sub.2, whereby the hot pipeline has an inner pressure p.sub.1 and is to be sealed off against the pressure p.sub.2 in the vessel.
When a hot pipeline extends out of a container that also contains a hot medium and when either the medium in the pipeline or the medium in the container is hotter, the pipe is made of what are called thermosleeves. The pipeline has a special structure where it extends through the container, in that the connection that is to extend out of the container is longer in diameter to accommodate interior insulation in conjunction with a protective pipe, followed by a section of pipe, again with a longer diameter, that extends parallel and in the opposite direction with its end welded to the opening through the container. The intermediate spaces are filled with a heat-insulating medium.
One of the drawbacks of thermosleeves is that the joint between the inner pipe and the container connection must be able to accommodate the stress of the interior pressure, which derives from the temperature difference and the weight of the components.